This invention relates to a method for manufacturing a heat transfer assembly. While the invention is particularly applicable to heat transfer devices of the type used in radiators for removing heat from the coolant in the cooling system of internal combustion engines, the invention in general is applicable to heat exchange devices where heat is transferred between liquid flowing through tubes and gases flowing through passages defined both by such tubes and by heat exchange fin strips associated therewith.
In the prior art method for manufacturing heat transfer devices of the type described above, a plurality of fin strips (typically made of copper) are formed, each of the fin strips being made from a unitary strip of metal folded back and forth to form a plurality of fin elements each having an essentially planar member between the fold edges. A plurality of substantially flat-sided metal tubes (typically made of brass) also are formed and, in past practice, these tubes have had a seam formed by interlocking crimped edges extending the length of the tube. Solder is used to seal the flat-sided tube. The fin strips and tubes are treated with a flux to remove surface oxidation and contaminants on the surface prior to the assembly of the fin strips and tube.
The fin strips and tubes are formed into a heat transfer assembly by placing a plurality of the tubes along side one another, by placing the fold edges on one side of a fin strip along the length of such tubes, and then by placing a second plurality of tubes on the fold edges on the opposite side of the fin strip, thereby, forming a sandwich construction. As many layers of tubes and fin strips as may be required may be stacked in this manner.
When the heat transfer assembly is to be used as a radiator for a motor vehicle, tanks are placed at opposite ends of the heat transfer assembly and are secured thereto so that coolant from the motor vehicle engine may enter one of the tanks, pass through the tubes and be cooled, and then enter the opposite tank from which it is withdrawn and then recirculated to the engine.
In manufacture of the heat transfer assembly, it is necessary to secure the fold edges of the fin strips to the flat sides of the tubes by soldering these together at such locations. The solder joint provides heat transfer from the tubes to the fin strips through thermal conductivity at such bond locations and the bonds also provide mechanical attachment of the fin strips to the tubes.
Prior art manufacturing processes have applied coats of solder to the entire exterior surface (and to crimped seams) of the tubes prior to their use in the heat transfer assembly. Once the assembly is made, the entire assembly, including tanks when the heat transfer assembly is used in a motor vehicle radiator, is placed in an oven where the solder on the tubes is caused to melt and thereby to flow to the locations of contact between the fold edges of the fin strips and the flat sides of the tubes. This produces the solder joints described above. Unfortunately, the solder that is on the tubes, but which does not constitute a part of the joint between the tubes and the fold edges of the fin strips is wasted, and also adds undesirable weight and manufacturing cost to the heat transfer assembly.